Synopsis British Airways flight 92 X-ray (BAW92X), a Boeing 747, was flying eastbound to London, England, along North Atlantic Track (NAT) Bravo at flight level 330 (FL330). At 1926 Coordinated Universal Time (UTC), the flight crew of BAW92X reported over St. Anthony, Newfoundland, with an estimate of 1950 UTC for the geographic fix of 5300'N latitude, 5000'W longitude (50 West); then, as instructed, they left the Gander Area Control Centre (ACC) frequency. Delta Air Lines flight 49 (DAL49), a Lockheed L1011, was flying westbound on NAT Bravo to Cincinnati, Ohio, also at FL330. At 1936 UTC, DAL49 passed by 50 West. The flight crew contacted the Gander ACC at 1942 UTC, at which time they requested and received a clearance to climb to FL350. At approximately 1944 UTC, 225 nautical miles northeast of Gander, DAL49 passed about 1,800 feet above and one mile south of BAW92X, where the required separation was 2,000 feet vertically. There were no injuries to crew or passengers. The Board determined that the controllers involved in this occurrence did not detect the traffic conflict between DAL49 and BAW92X prior to the risk of collision. Contributing to this occurrence were the controllers' loss of situational awareness created by complacency and a lack of vigilance during a period of low-traffic activity. 1.0 Factual Information 1.1 History of the Flight At 1926 Coordinated Universal Time (UTC) 1, British Airways flight 92 X-ray (BAW92X)2, a Boeing 747, passed over St. Anthony, Newfoundland (NFLD), flying at flight level 330 (FL330) eastbound to London, England, along North Atlantic Track (NAT) Bravo. The flight crew called Gander Area Control Centre (ACC) with their position report and gave an estimate of 1950 for the geographic fix 5300'N latitude, 5000'W longitude (50 West). Gander ACC acknowledged the estimate and, at 1926:35, instructed the flight crew to change to another frequency. Delta Air Lines flight 49 (DAL49), a Lockheed L1011, passed over 50 West at 1936, flying westbound at FL330 along NAT Bravo to Cincinnati, Ohio. At 1942, the flight crew of DAL49 contacted Gander ACC for the first time. The flight crew requested and received a clearance to climb to FL350. As DAL49's first officer entered the new altitude into the aircraft's vertical navigation computer, he observed conflicting opposite-direction traffic at 30 miles on the Traffic Alert and Collision Avoidance System (TCAS). The crew expedited the climb in order to avoid the conflicting traffic. DAL49 passed about 1,800 feet above and one mile south of BAW92X, where the required separation was 2,000 feet vertically. The two aircraft had been closing at a combined speed of 980 knots, and at 30 miles were less than two minutes apart. The occurrence took place at 5225'N, 5240'W at approximately 1944, during daylight hours. (See Appendix A.) 1.2 Injuries to Persons 1.2.1 Delta Air Lines Lockheed L1011 N740DA 1.2.2 British Airways Boeing 747 G-AWNH 1.3 Damage to Aircraft There was no damage to either aircraft. 1.4 Other Damage 1.5 Personnel Information 1.5.1 Air Traffic Controller Information 1.6 Aircraft Information 1.7 Meteorological Information Both aircraft were operating under instrument flight rules (IFR) in visual meteorological conditions (VMC) at the time of the occurrence. The crew of DAL49 had visual contact with BAW92X as it passed below their aircraft. 1.8 Aids to Navigation There were no reported discrepancies with the navigational aids being used by the aircraft involved in this occurrence. In addition, there were no reported discrepancies with the equipment being used by the Gander ACC controllers. 1.9 Communications Communications between the Gander ACC and the aircraft were reported to be normal before, during, and after the occurrence. 1.10 North Atlantic Tracks Air traffic control over the North Atlantic Ocean is handled primarily from Gander, Newfoundland, and Prestwick, Scotland. Primary responsibility for the planning function of the eastbound flow, which predominates at night between 2300 and 0500 UTC, rests with Gander, and for the westbound flow, which predominates during the daytime between 1000 and 2100 UTC, with Prestwick. In order to regulate the flow during peak traffic periods, discrete tracks and altitudes are instituted. Conflict detection on these tracks over the ocean, east of 50 west longitude, up to 52 north latitude, is provided by the Gander automated air traffic system (GAATS). By using GAATS, the planner is alerted to any conflict with other oceanic traffic when an aircraft's flight plan is entered into the computer. Conflict detection in domestic airspace is the responsibility of the controller and is achieved by utilizing radar, flight progress strips, and pilot position reports. This risk of collision took place in a small area of domestic airspace where there is no radar coverage; the controller must rely on information from the flight progress strips to provide separation. It is possible for as many as 400 aircraft to transit the Gander Domestic airspace during the peak four hours of eastbound or westbound flow. During the changeover periods from day to night tracks, traffic volume and controller workload is considerably reduced. This daily change in traffic volume is generally consistent and is anticipated by the controllers. 1.11 Flight Progress Strips The most basic form of controlling air traffic consists of monitoring a flight data board displaying flight progress strips, a paper strip for each aircraft's flight data. This data is updated manually by the controller from position reports received from aircraft. Flight progress strips are arranged in bays under fix designators corresponding to the geographic location of a navigational fix. A flight progress strip depicting an aircraft's route of flight and altitude is placed under the fix designator that will best indicate the geographic position of the aircraft so that potential traffic conflicts can be more easily recognized and accurately assessed. In Gander ACC, flight progress strips for westbound aircraft are printed in red ink, while strips for eastbound aircraft are printed in black ink. For some time prior to the occurrence, there were only two aircraft flight progress strips under the St. Anthony fix designator. One strip was for the westbound DAL49 at FL330 and the other was for the eastbound BAW92X, also at FL330. The ATC Manual of Operations (MANOPS), Appendix 2, explains flight progress strip marking for IFR operations. Section 1.1.8 describes the controller's on-going scan of the control data board as follows: Scan the control data board by performing the following actions: scan each bay individually rather than looking over the entire board; in each bay, check altitude boxes to verify vertical separation; if more than one aircraft is at the same altitude, check strips to ensure some other form of IFR separation exists; follow individual flights through the sector, checking for conflicting, converging or crossing track situations, consistency in altitude and estimate data, and for correct posting. 1.12 Traffic Conflict Detection There were four opportunities for different controllers in Gander ACC to detect the traffic conflict developing between DAL49 and BAW92X. Procedures, standards, guidelines, and checklists are available for the controllers to ensure the safe separation of aircraft. The separation standard that should have applied in this case was 2,000 feet vertically between the two aircraft. Staffing in the Gander ACC during the occurrence met unit standards. 1.12.1 Oceanic Planner Controller The first opportunity to detect the conflict occurred when the oceanic planner initially received the requested altitude, FL330, for BAW92X. He coordinated this altitude with Prestwick centre and entered the information into GAATS. GAATS did not show a conflict between BAW92X and DAL49 because DAL49's estimated time of arrival (ETA) for 50 West was earlier than BAW92X's ETA for 50 West. The planner did not check with the Gander oceanic controller to determine if FL330 was okay for BAW92X because he saw that the oceanic controller was busy with a trainee. The planner checked the ocean data board himself and, although the data showed a conflict with DAL49 already at FL330, he did not detect the conflict. He returned to his position and the flight progress strip for BAW92X was produced at 1901. 1.12.2 High-Level Domestic Controller A second opportunity to detect the conflict occurred when the Gander high-level domestic controller received the flight progress strip in black ink for BAW92X about 1845 and put it on the control data board under the St. Anthony fix designator along with the flight progress strip in red ink for DAL49. He did not detect the conflict during his routine scan of the control data board prior to being relieved at the sector. 1.12.3 High-Level Domestic Controller Instructor and Trainee The third opportunity to detect the conflict occurred when the high-level domestic radar controller was relieved by a high-level domestic on-the-job instructor (OJI) and his trainee about 1915. The relieving controllers followed the standard Gander ACC procedure of first standing behind the position to observe the traffic. Next the relieving controllers were briefed, and a data board check was performed by the controller at the position. The briefing is designed to follow a written checklist and includes altitude reservations, separation problems to be resolved, conflicts, and immediate control actions. The relieving controller then sits at the sector position while the controller being relieved stands behind the position and observes until the relieving controller is acclimatized to the sector. Controllers regard the sector briefing as common sense, and they report that the written checklists disappear from the control positions within a matter of days or weeks. In this case, the relieving controllers reported that they did observe the sector and get a briefing, and that the relieved controller did stand behind them for some time. The traffic conflict between BAW92X and DAL49, the only two data strips under the St. Anthony fix designator, was not detected at this time. The controllers reported that the sector briefing pointed out that most of the traffic was over the tracks in the southern airspace of the Gander area. The sector's radar was displaying mostly traffic on the tracks in the southern, rather than northern, part of the airspace. The OJI reported that the trainee sat in at the high-level domestic position after receiving the briefing, and the OJI observed the trainee do a data board check; the OJI also did a scan of the data board. Prior to the occurrence, the trainee was responsible for five or six aircraft at any one time that were transiting through his sector. This traffic volume was assessed as light to moderate. Review of the sector's audio tape recording for the 30 minutes prior to the occurrence indicated nine aircraft on the frequency and a period of almost seven minutes with no radio transmissions just prior to the occurrence. At 1926, BAW92X contacted the Gander ACC trainee with a position report over St. Anthony. The trainee had already marked BAW92X's data strip when he accepted the handoff from west radar and, nine minutes later, he wrote the aircraft's progress report on the flight data strip. The aircraft reported maintaining FL330 and the trainee told the pilot to contact Gander Radio in 100 miles. The trainee did not detect the conflict on the two strips under the St. Anthony fix designator, the red one for DAL49 and the black one for BAW92X, both marked at the same altitude. At 1942, DAL49 contacted the Gander ACC trainee and reported at FL330, with an estimate for St. Anthony of 2019. The trainee issued the aircraft a domestic clearance and asked the pilot of DAL49 what altitude they were requesting. At that point the controllers realized that both DAL49 and BAW92X were at FL330, on the same track and possibly in conflict. After confirming that DAL49 was at FL330, the trainee cleared the aircraft up to FL350. The clearance to DAL49 did not include an instruction to expedite the climb or any traffic advisory about the position of BAW92X. 1.12.4 Oceanic Controller The fourth opportunity to detect the conflict occurred when an oceanic controller took over the ocean sector from the first oceanic controller and his trainee at about 1905. When the relieving controller did his data board check, he did not notice that the flight data strips for DAL49 and BAW92X indicated that the aircraft were at the same altitude, travelling in opposite directions, on the same track. About 1915, a second strip for BAW92X was produced with a speed change and no change to the routing. The oceanic controller received this new strip and compared it with the BAW92X strip already on the board. Once again, he did not detect the conflict with DAL49. The oceanic controller also did not detect the traffic conflict during his routine scan of the data board. 1.13 Controller Situational Awareness Studies have shown that controllers form a mental picture of air traffic that assists with the conceptualization and prediction of aircraft movement. Information used to develop this picture comes from radar displays, aircraft position reports, and the data from flight progress strips. Maintenance of the picture is essential for controller situational awareness and effective air traffic control. David Hopkin, in his book Situational Awareness in Complex Systems (Embry-Riddle Aeronautical University Press, 1994), makes the following observations about situational awareness in air traffic control: Situational awareness will be subject to the formation of habits, may be resistant to new evidence that appears to contradict what is already known, may be biased in the choice of what is relevant to it, and may be influenced, and perhaps overly influenced by memories which once recalled, may be treated as more relevant than they are. All the major proposed forms of computer assistance for air traffic controllers in performing their tasks, and all the intended forms of automation in air traffic control that are envisaged to have some consequences for the controller, must affect situational awareness. The reason is that all aids require new learning of some kind and situational awareness is a function of learning. The expressed anxieties about some of the consequences for situational awareness of increased air traffic control automation, such as an increased propensity for the controller to lose the picture or reduced controller understanding of the picture, seem to have some justification. 1.14 Controller Vigilance In 1990, the Canadian Aviation Safety Board (CASB), as a result of a special investigation into air traffic control services, stated that inattention or lack of vigilance appears to be contributory in approximately 50 per cent of all air traffic services (ATS) occurrences, and that these types of errors often happen during periods of light, non-complex traffic. Complacency and boredom were considered to contribute to the frequency of attention-related occurrences.